Multi-media systems typically require the mixing and scaling of audio signals. Traditionally, these operations are performed in the analog domain with switched capacitor circuits. Such conventional circuits typically provide analog mixing and scaling of one or more signals either through a switched capacitor circuit or resistor circuit, followed by oversampling in a delta sigma converter to convert the mixed and scaled signal to the digital domain as a pulse density demodulated (PDM) signal.
A drawback of conventional analog scalars is that they require a ratio of capacitors or resistors approach to scaling. It can be difficult to achieve exact scaling with such circuits, which require very accurately matched components. Another drawback is that in conventional systems a signal to noise ratio of a composite signal is degraded in proportion to the number of signals comprising the composite signal. Still another drawback is that conventional circuits degrade the signal to noise ratio of input signals. Thus, there is a need for a circuit that can achieve mixing and scaling of audio signals in the digital domain.